Lighting system and liquid crystal backlight device

ABSTRACT

Luminance irregularities caused by the weight of the optical members in a backlight apparatus are reduced. A lighting apparatus comprises optical members  1  and  2 , a casing in which the optical members  1  and  2  and a lamp  4  are disposed, a first member  1   a  formed in optical members  1  and  2 , and a second member  3   a  formed in the casing for attaching the optical members  1  and  2  to the casing by cooperating with the first member  1   a . The first and second members  1   a  and  3   a  are provided in positions such that no upward stress is applied to the optical members due to their own weights at the bottom in a vertical direction in the plane of the display screen, both in a basic position and a first stop position of the lighting apparatus, the latter position being reached by rotation of the apparatus from the basic position in the plane of the display screen.

TECHNICAL FIELD

The present invention relates to a lighting apparatus and a liquidcrystal display (“LCD”) apparatus using the same, particularly to abacklight apparatus for large-sized LCD apparatuses.

BACKGROUND ART

Referring to FIGS. 14 and 15, in some conventional LCD backlightapparatuses, an opening 2 a is provided on an upper section of opticalsheets 1 and/or a diffusing plate 2 (which will be referred to asoptical members) towards either side. Locking portion 3 a are providedin a frame 3 at positions corresponding to openings 2 a, so that theframe can support the optical members.

DISCLOSURE OF THE INVENTION

If the optical members such as optical sheets and a diffusing plate arelocked with the frame merely at the upper-side portions of the screen ofthe LCD apparatus, problems may arise when the screen of the LCD isrotated on its normal axis (in-plane rotation), for example.

Specifically, if the display in this case is rotated in the plane of thescreen and turned upside-down, the openings of optical members will belocated at either side of the lower half of the screen. This can causethe optical members to be warped or curved due to their own weights,particularly when the optical members are large (for large screensizes).

If the curving or warping of the optical members become excessive, thediffusing plate, for example, could come into contact with some parts ofthe LCD panel via the optical sheets. This causes heat to be transferredfrom the diffusing plate to the LCD panel, resulting in temperaturedifferences on the LCD panel between where it is in contact with thediffusing panel and where it is not. These temperature differencesproduce unintended luminance or contrast irregularities on the LCDpanel. Further, as the size of LCD apparatuses increase, such warping orcurving can result in problems in the structure of the apparatus or inmanufacturing processes.

It is therefore an object of the invention to provide a structure inwhich the warping or curving of the optical members is prevented whenthe display is rotated, so that display luminance irregularities can bereduced.

In one aspect, the invention provides a lighting apparatus comprising:

an optical member;

a casing in which the optical member and a lamp are disposed;

a first member provided in the optical member; and

a second member provided in the casing for attaching the optical memberto the casing by cooperating with the first member, wherein

the first and second members are disposed such that both when thelighting apparatus is in a basic position and in a first stop positionreached when the lighting apparatus is rotated from the basic positionin the display plane, no upward stress is applied to a lower part of theoptical member in the plane of the display screen due to its own weight.

The first member may be an opening (hole) formed in the optical member,for example, and the second member may be a locking projection forattaching the optical member to the casing via the opening.

In another aspect, the invention provides a lighting apparatuscomprising:

an optical member;

a casing in which the optical member and a lamp are disposed;

a first member provided in the optical member; and

a second member provided in the casing for attaching the optical memberto the casing by cooperating with the first member, wherein

the first and second member are disposed such that both when thelighting apparatus is in a basic position and in a first stop positionreached when the lighting apparatus is rotated from the basic positionin the plane of the display screen, the optical member is supported atthe top in the plane of the display screen, and no upward stress isapplied to the optical member at the bottom due to its own weight.

In this lighting apparatus, the optical member is prevented from beingeasily warped when rotated to different positions from the basicposition.

Preferably, in the state where the opening or the edge of cutaway at thebottom of the non-effective screen range of the LCD apparatus does notcontact the locking projection, a degree of spatial freedom is givenbetween the opening or the edge of cutaway and the locking projectionthat are not locked with one another.

In another aspect, the invention provides a rotatable LCD apparatuscomprising:

an LCD apparatus; and

a rotating mechanism for rotating the LCD apparatus, wherein the LCDapparatus includes an LCD backlight apparatus and an LCD panel, the LCDbacklight apparatus comprising:

an optical member in which a plurality of openings or cutaways areformed above and below the center of gravity of the optical member; and

a casing in which the optical member and a lamp are disposed, the casingincluding a locking projection that abuts on the openings or cutaways tothereby support the optical member, and a locking projection that doesnot abut on the openings or cutaways, wherein the openings or the edgesof the cutaways do not contact the locking projections below the centerof gravity in either a basic position or in a first stop position of theLCD apparatus, the first stop position being reached as the LCDapparatus is rotated from the basic position in the plane of the opticalmember, wherein the LCD panel is disposed on the opposite side of theoptical member from the lamp. This apparatus is capable of providingclear display in any of the rotation positions.

In a further aspect, the invention provides a lighting apparatuscomprising:

an optical member; and

a casing in which the optical member and a lamp are disposed, wherein

the optical member can be locked above and below the center of gravityin a vertical direction depending on its rotation, wherein the opticalmember is adapted not to receive upward stress below the center ofgravity. Thus, the influence of the weight of the optical members can bereduced in any of the rotation positions.

Thus, deformation such as warping or curving of the optical sheetsand/or diffusing plate can be prevented in any position of the display.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1(A) and (B) are drawings for the explanation of the principle ofthe LCD backlight apparatus according to an embodiment of the invention.

FIG. 2 shows a broken perspective view of the LCD backlight apparatusaccording to a first embodiment of the invention.

FIG. 3(A) shows a front view of the LCD backlight apparatus shown inFIG. 2, and FIG. 3(B) shows a cross-sectional view taken along lineIII-III of FIG. 3(A).

FIGS. 4(A) and (B) show the LCD backlight apparatus according to thefirst embodiment of the invention as it is rotated to various angles.

FIGS. 5(A) and (B) show the LCD backlight apparatus according to thefirst embodiment of the invention as it is rotated to various angles.

FIG. 6 shows a broken perspective view of a first variation of the firstembodiment of the invention.

FIG. 7(A) shows a front view of the LCD backlight apparatus of FIG. 6,and FIG. 7(B) shows a cross-sectional view taken along line VII-VII ofFIG. 7(A).

FIG. 8 shows a broken perspective view of the LCD backlight apparatusaccording to a second variation of the first embodiment of theinvention.

FIG. 9(A) shows a front view of the LCD apparatus of FIG. 8, and FIG.9(B) shows a cross-sectional view taken along line IX-IX of FIG. 9(A).

FIG. 10 shows a broken perspective view of the LCD backlight apparatusaccording to a second embodiment of the invention.

FIG. 11(A) shows a front view of the LCD backlight apparatus shown inFIG. 10, and FIG. 11(B) shows a cross-sectional view taken along lineXI-XI of FIG. 11(A).

FIGS. 12(A) and (B) show the LCD backlight apparatus according to athird embodiment of the invention.

FIG. 13 shows an example of an optical member (diffusing plate) in theLCD backlight apparatus according to a fourth embodiment of theinvention.

FIG. 14 shows a broken perspective view of a conventional LCD backlightapparatus.

FIG. 15(A) shows a front view of the LCD backlight apparatus shown inFIG. 14, and FIG. 15(B) shows a cross-sectional view taken along lineXV-XV of FIG. 15(A).

FIG. 16(A) shows a front view of an LCD television according to anembodiment of the invention, and FIG. 16(B) shows a rear view of the LCDtelevision.

FIG. 17 shows the relationship between the number of days an opticalmember was left immersed in water and the water absorption ratio.

FIG. 18 shows the relationship between the saturation absorption and thelength-increasing ratio of an optical member.

BEST MODE FOR CARRYING OUT THE INVENTION

In the present specification, when referring to the positions of theopenings and locking projections, the “top” of the display screen refersto an upper part of the screen vertically above with respect to thecenter of gravity of the optical members. When a backlight is used in anLCD apparatus, the openings and locking projections are usually providedat the edge portions of the display screen. Therefore, the “top” usuallyrefers to the upper or lower edges (frame edges) of the display screen.Further, in the present specification, the term “casing” includes theframe, shields, a reflecting plate, and a lamp holder. The lockingprojections are provided on the casing. The casing may not include alamp.

Referring to FIGS. 16(A) and (B), a rotatable LCD television will bedescribed. As shown in FIG. 16(A), a rotatable LCD television 100includes a main body 101 and a stand 103. The main body 101 includes adisplay screen 102 and a frame 105. Various operation buttons 107 areprovided in the frame 105. The main body 101 and stand 103 are connectedby a support 103 a.

As shown in FIG. 16(B), the support 103 a and the main body 101 arecoupled by a rotation mechanism 115 on the back of the rotatable LCDtelevision, such that the main body 101 is rotatable in the plane of thedisplay screen 102. The television has at least two stop positions,i.e., a first stop position 101 a and a second stop position 101 b, sothat a viewer can watch TV on a screen which is longer in either thehorizontal or vertical direction.

Before describing the embodiments of the invention, the analysisconducted by the inventors will be discussed by referring to FIGS. 1(A)and (B). In the apparatus as shown in FIG. 16, in which the LCD can berotated so as to provide a plurality of viewing positions, the inventorsrecognized the need to reduce the warping or curving of the opticalmembers at each of the stop positions so that the display irregularitiescould be reduced.

Referring to FIG. 1(A), a total of four openings, namely openings 2 a-1(two at the top) and openings 2 a-2 (two at the bottom), are provided inthe optical members (including optical sheets) attached to the frame(not shown). Locking projections 3 a-1 for supporting the opticalmembers 1 are provided on the frame such that they can be freely fittedinto the openings 2 a-1.

Both before and after rotation of the LCD apparatus by 180° in the planeof the display screen as shown in FIG. 1B (the position prior torotation, as shown in FIG. 1(A), is the default position and will bereferred to as the “basic position” hereafter), it is desirable that twoconditions be met. Condition 1 is that, of the openings 2 a-1 or 2 a-2and locking projections 3 a-1 or 3 a-2, the openings and the lockingprojections located at the top be positioned relative to one anothersuch that an upper edge portion of each opening abut (is locked by) anupper periphery portion of a corresponding locking projection. A second(subordinate) condition is that the openings a corresponding lockingprojection at the bottom be positioned relative to one another such thatthe upper peripheral portion of each locking projection does not abutthe upper edge of a corresponding opening (a “freely fitted state”) inthe normal range of use, or that it abuts but only to such an extentthat no warping or curving would be caused in the optical members due tothe stress applied to the optical members in a vertically compressingdirection. As the optical members such as optical sheets and thediffusing plate are subject to thermal expansion due to temperatureincreases, it is desirable that conditions 1 and 2 be met even in theevent of thermal expansion.

The viewer may wish to rotate the LCD apparatus by 90° in the displayplane. To allow for such cases, the optical members are provided withopenings 2 a-3 and 2 a-4 at four locations along the vertical sides ofthe members. Likewise, the frame is provided with four lockingprojections 3 a-3 and 3 a-4 for supporting the optical members. Bothbefore and after rotation by 90° or 270°, it is desirable that the upperedge of each of openings 2 a-3 or 2 a-4 abuts on the periphery of acorresponding locking projection 3 a-3 or 3 a-4 at the top, to satisfycondition 1. It is also desirable that the openings and lockingprojections at the bottom not abut on each other but rather be in afreely fitted state in the normal range of use of the LCD apparatus, orthey abut on each other but only to such an extent that no warping orcurving would be caused in the optical members, thereby satisfyingcondition 2. Desirably, both conditions 1 and 2 should be satisfied evenin the event of thermal expansion of the optical sheets or diffusingplate due to temperature rises.

The number and positions of the openings and locking projections mayvary depending on the degree to which the LCD apparatus is expected tobe rotated.

Still referring to FIGS. 1(A) and (B), the positional relationshipsbetween the openings and locking projections will be described in moredetail, by referring to an example of an LCD backlight apparatus. As theprocess of deformation differs between the optical sheets 1 and thediffusing plate 2, their design values must also be varied to accomodatethe deformation. However, they can be considered similar in terms ofpositional relationships between locking projections and openings. Thus,the openings formed in the optical members such as the optical sheets 1and diffusing plate 1 and the locking projections should have thefollowing relationships. Namely, when providing play between theopenings and the locking projections, the amount of elongation of thediffusing plate or optical sheets and the condition concerning thelocking at the top of a non-effective screen range of the LCD apparatusshould be considered.

The distance between the upper and lower edges of an opening will bereferred to as d1, and the distance (thickness) between the upper andlower peripheries of a locking projection will be referred to as d2. Thediffusing plate 2 is mounted on the frame 3 as the upper edge of opening2 a-1 abuts the upper periphery of locking projection 3 a-1 that hasbeen inserted into the opening. A distance y′ between the lower edge ofopening 2 a-2 and the lower periphery of locking projection 3 a-2 isexpressed by:y′=L1-L2where L1 is the distance between the upper edge of opening 2 a-1 at thetop and the lower edge of opening 2 a-2 at the bottom, and L2 is thedistance between the upper periphery of locking projection 3 a-1 at thetop and the lower periphery of locking projection 3 a-2 at the bottom.

Under these definitions, a case will be considered in which thediffusing plate 2 has extended to a maximum in the normal range of useof the LCD apparatus (involving the generation of heat by keeping thelamp on for a long time), in view of the thermal expansion property ofthe diffusing plate 2, for example. In this case, the distance betweenthe upper edge of opening 2 a-1 at the top and the lower edge of opening2 a-2 at the bottom will be designated as L1′. The amount of play ymaxcan be expressed by ymax=L1′-L2. There should be a degree of freedomsuch that the diffusing plate 2 can be moved by the amount of play ymaxwhen the backlight set is turned upside-down. This condition can beexpressed by0<ymax<(d1-d2)  (9-1)ymax=L1′-L2=L1+ΔLy-L2  (9-2)where ΔLy is the maximum amount of elongation in the distance betweenthe upper edge of opening 2 a-1 at the top and the lower edge of opening2 a-2 at the bottom.

From expressions (9-1) and (9-2), L1-L2=ymax-ΔLy<d1-d2-ΔLy, which givesL1-L2<d1-d2−ΔLy  (9-3)

Thus, it is necessary to make the difference between d1-d2 and ΔLy,which is the decrease in d1-d2 when elongation is taken into account,larger than L1-L2 prior to elongation.

Hereafter, the positional relationships between openings 2 a-3 and 2 a-4located on the left and right sides of the diffusing plate 2 andcorresponding locking projections 3 a-3 and 3 a-4 will be described. Twoof these positional relationships in the vertical and horizontaldirections should be considered. With regard to the vertical direction,play between the openings 2 a-3 and 2 a-4 and the locking projections 3a-3 and 3 a-4 on the left and right sides should be taken to be widerthan ymax. This can be expressed byt2>ymax=L1′-L2=(L1-L2)+ΔLy  (9-4)where t2 is the distance between the bottom edge of each opening 2 a-3or 2 a-4 and the bottom edge of a corresponding locking projection 3 a-3or 3 a-4 when the diffusion plate has been elongated to the greatestextent.

With regard to the horizontal direction, play in the vertically adjacentopenings (2 a-3 and 2 a-3, or 2 a-4 and 2 a-4) and play in thehorizontally opposite openings (2 a-3 and 2 a-4) should be designed bytaking the elongation of the diffusing plate 2 into consideration. Asshown in FIG. 1(B), this can be expressed byW1-W2>ΔWx(W1)≈ΔWx(W2)  (9-5)W3-W4>ΔWx(W3)≈ΔWx(W4)  (9-6)where W1 is the distance between the inner sides of the adjacent lockingprojections at the top (or bottom) in a normal state, W2 is the distancebetween the inner sides of the adjacent openings at the top (or bottom)in a normal state, W3 is the distance between the inner sides of thehorizontally opposite locking projections in a normal state, W4 is thedistance between the inner sides of the horizontally opposite openingsin a normal state, and ΔWx(Wn) is the maximum amount of elongation inlength Wn (n=1, 2, 3, or 4).

The positional relationship between the openings of the diffusing plate2 and the locking projections 3 can be designed based on expressions(9-3) to (9-6). Positional relationships can be similarly calculated fora 90° rotation of the LCD apparatus (backlight) in the display plane.The optical sheets can also be designed in the same manner as for thediffusing plate 2.

Hereafter, an example of the method of calculating the amount ofelongation of the diffusing plate ΔL will be described. In this example,the elongation of the diffusing plate of a direct backlight in a 20-inchLCD apparatus will be considered. The diffusing plate of the directbacklight for 20-inch size measures 400 mm×300 mm×2.0 mm. Four openingsare provided in the diffusing plate, two at the top and two at thebottom. The interval between the horizontally opposite openings is 200mm. The following data is based on a technical data booklet “SMIPEX”compiled by Sumitomo Chemical Co., Ltd., Methacrylates and OpticalProduct Division.

In general, plastics materials expand against heat, and the higher thetemperature, the greater the expansion. Accordingly, this property mustbe considered when designing the positions of the openings in thediffusing plate 2. If there is not enough spatial degree of freedom(gap) between the diffusing plate 2 and the locking projections at roomtemperature, the interval between the left and right openings in thediffusing plate 2 becomes larger. If this interval becomes greater thanthe interval between the left and right locking projections, theopenings would come into contact with the locking projections and thediffusing plate 2 could even be deformed (such as by warping). Thus, thegap (play) between the openings in the diffusing plate 2 and the lockingprojections should be calculated in the following manner.

In general, the ease with which plastics expand due to temperatures isexpressed by linear expansion coefficient (unit: 10⁻⁵/° C.). Assumingthat the linear expansion coefficient is constant with respect totemperature, and that the linear expansion coefficient of acrylicmaterials is about 7.0, the temperature around the diffusing platebecomes 60° C. at maximum, considering the temperature range of the LCDpanel in use. In light of these temperature environments, the extensionin the interval between the left and right openings in the diffusingplate at room temperature can be calculated as follows:(Extension in the diffusing plate)=(linear expansioncoefficient)×[(temperature around the diffusing plate)−(roomtemperature)]×(length at room temperature)

Specifically, ΔL=(7.0×10⁻⁵/° C.)×(60° C.−20° C.)×(20cm)=5.6×10⁻³(cm)˜0.6 mm.

Thus, it can be estimated that the interval between the two openings inthe diffusing plate 2 would expand by about 0.6 mm horizontally.Accordingly, by providing an interval between the locking projectionsand the openings such that they do not abut on each other in the eventof expansion of the diffusing plate 2 by about 0.6 mm horizontally, thewarping of the diffusing plate 2 due to its thermal expansion causingthe openings to abut on the locking projections, which in turn press theedge of the openings, can be prevented. Similar calculations can be maderegarding the vertical direction. In reality, temperature tests can beconducted using actual samples so that the warping of the opticalmembers can be reliably prevented. The warping of the optical membersdue to heat expansion of the diffusing plate or the like can beprevented by estimating the necessary gap between the openings andlocking projections at the design stage.

In the following, a direct LCD backlight apparatus according to a firstembodiment of the invention will be described by referring to FIGS. 2 to3(B) illustrating the structure of the apparatus. FIG. 2 is an explodedperspective view of the direct LCD backlight apparatus. FIG. 3(A) is apartially cutaway front view of the structure of the optical sheets anddiffusing plate. FIG. 3(B) is a cross section taken substantially alongline III-III′ of FIG. 3(A), showing the structure including thediffusing plate, optical sheets, LCD panel, and a frame fixing the LCDpanel in place.

As shown in FIGS. 2 to 3(B), the backlight apparatus includes variousoptical sheets 1, a diffusing plate 2, a shield 3, a lamp 4, a lampholder 5, a reflecting plate 6, and an LCD panel 7. The optical sheets 1and the diffusing plate 2 are provided with openings 2 a (at 8 locationseach on the optical sheets and the diffusing plate) in the peripheral,non-effective display-screen portions thereof. The shield 3 and the lampholder 5 are provided with locking projections 3 a at locationscorresponding to the openings 2 a such that the locking projections canenter the openings 2 a. Preferably, the locking projections 3 a may beprovided in the side portions of the shield 3 instead of or togetherwith the lamp holder 5.

The positional relationships between the locking projections 3 a and theopenings 2 a are designed such that at least the openings 2 a andlocking projections 3 a at the bottom do not abut on each other, or suchthat they abut only to an extent that neither the optical sheets 1 northe diffusing plate 2 warp. In this way, the warping or deformation ofthe optical sheets 1 or diffusing plate 2 due to their own weight, forexample, can be prevented. If one or both of the optical sheets 1 andthe diffusing plate 2 are locked at the bottom of the display, the pointof application of force in the event of deformation of the opticalsheets 1 or diffusing plate 2 by their own weights would be at thelocked position. This would cause the reaction force to be applied abovethe point of support, namely the screen as a whole, resulting indeformation such as warping.

Conversely, the higher the location of the locking projections forsupporting the optical members, the narrower the region influenced bythe reaction force, i.e., the region above the locking positions, wouldbe, so that the deformation of the optical members due to their ownweights would become less likely. In particular, when the optical sheets1 or diffusing plate 2 are locked at the openings formed in anon-effective screen region, little warping occurs in the opticalmembers due to their own weights even when the area of the displayscreen is increased.

FIGS. 4 and 5 show the positional relationships between the openings inthe optical members and the locking projections as the LCD backlightapparatus is rotated in the display plane. Hereafter, the positionalrelationships between the openings and the locking projections will beconsidered as the LCD backlight apparatus is rotated by 180° (turnedupside-down) as shown in FIG. 4(B) from the basic position shown in FIG.4(A), by 90° clockwise as shown in FIG. 5(A), and by 270° clockwise asshown in FIG. 5(B). In any of these cases, it is desirable that theupper edge of each opening abuts that of each corresponding lockingprojection at the top, while the edge of each opening and thecorresponding locking projection at the bottom do not abut on each otheror they abut but only to such an extent that the optical members wouldbe hardly pressed. In this way, the optical members can be preventedfrom warping at each of the 90°, 180°, and 270° rotational positions.

For example, in the basic position shown in FIG. 4(A), the openings 2a-2 at the bottom are freely fitted with the locking projections 3 a-2,which is true in any of the 180° position in FIG. 4(B), 90° position inFIG. 5(A), and 270° position in FIG. 5(B).

In the LCD backlight apparatus shown in FIGS. 2 to 5, each side isprovided with two openings. Preferably, however, the number of openingson each side may be increased or decreased depending on the length ofeach side of the optical sheets 1 or diffusing plate 2, or depending onlocking stability. For example, each side may be provided with a singleopening.

Next, a variation of the first embodiment of the invention will bedescribed by referring to FIGS. 6(A) to 7(C), which correspond to FIGS.2 to 3(B). In this variation, the LCD backlight apparatus is providedwith one opening 2 a and one locking portion 3 a in each corner thereof.In this configuration, as shown in FIGS. 6 to 7(B), each side has anopening 2 a on either end, so that only four openings 2 a are requiredin the diffusing plate of the rectangular LCD backlight apparatus, thusreducing the number of openings and locking projections. Yet in thissimplified embodiment with less openings, the number of lockinglocations at any particular stop position does not change from the firstembodiment.

Hereafter, a second variation of the first embodiment of the inventionwill be described by referring to FIGS. 8 to 9(B). As shown in FIGS. 8to 9(B), two locking projections are provided in each of the four sidesof the substantially rectangular frame and/or lamp holder, for a totalof 8 locking projections. On the other hand, the diffusing plate 2 isprovided with a cutaway portion 21 on each of the four sides thereof,each cutaway portion having a width substantially corresponding to thedistance between the outer edges of the two locking projections 3 a oneach side of the frame or lamp holder. Thus, while the optical sheets 1are formed with openings 2 a, the diffusing plate 2 is formed not withopenings but with the cutaway portions 21 along each side. The frame andthe diffusing plate are united as the periphery of each lockingprojection 3 a abuts each end of the cutaway portions 21. While inreality the lockable cutaway portions are provided at two locations ineach side of the non-effective screen region, one may preferably beprovided for each side if this does not influence the deformation of theoptical sheets 1 or diffusing plate 2.

In the present variation, the optical members are supported by the upperedges of the cutaways on the left and right sides thereof abutting thelocking projections, instead of their being supported at the top of thenon-effective screen region. However, there is a possibility that, whenthe cutaway portions are provided on the left and right sides at aboutthe height of the center of the display, warping might occur in theoptical sheets 1 or diffusing plate 2 above the locking positions due totheir own weight, particularly when the size of the display is large, asdescribed above. To prevent this, the length of the cutaway in each sideis extended in this variation, and the locking projections arepositioned at either end of the cutaway. In this way, the warping of theoptical members at the top can be minimized.

Hereafter, the LCD backlight apparatus according to a second embodimentof the invention will be described by referring to FIGS. 10 to 11(B). Asthe size of the LCD increases, so does the size of the optical sheets 1and the diffusing plate 2, resulting in an increase in their weight.However, as the optical members such as the optical sheets are made ofplastic, there is a limit to their mechanical strength. Thus, theopenings formed in these members could be deformed by the weight of themembers.

Therefore, it is necessary to design the openings such that they canwithstand the stress caused by the members in which they are provided.This is achieved by increasing the area of contact between the openings2 a formed in the optical sheets 1 or diffusing plate 2 and the lockingprojections 3 a. Specifically, the abutting portions of the openings 2 aand the locking projections 3 a are elongated along the side(horizontally). As described above, in the LCD backlight apparatusaccording to the embodiments of the invention, the diffusing plate 2 islocked by the locking projections located at the upper end of the shield3. As a result, the upper edge of the openings of the diffusing plate 2is subject to stress corresponding to the weight of the diffusing plate.Therefore, by increasing the length of the openings 2 a and the lockingprojections 3 a at the top along a direction (along the side)perpendicular to the direction of application of the weight of thediffusing plate, the area of contact between the openings 2 a and thelocking projections 3 a can be increased.

In this structure, the stress due to the weight of the diffusing plate 2applied to the upper edge of the openings 2 a can be distributed over anextensive contact plane, so that the deformation of the optical memberscaused by their own stress can be prevented. Desirably, the lockingprojections and the openings at the bottom should also be configured ina similar manner so as to increase their area of contact, as the loweredges of the openings would be subject to a similar stress when the LCDapparatus (LCD backlight apparatus) is rotated by 180° (turnedupside-down), for example, in the display plane.

The openings and locking projections on the left and right sides withrespect to the normal orientation (basic position) can be considered ina similar manner when the LCD apparatus is rotated by 90° in the displayplane. Specifically, the area of contact between the openings 2 a andlocking projections 3 a can be increased by elongating them in avertical direction in the basic position (along the left and rightsides), so that the stress put on the optical members can bedistributed.

Hereafter, a third embodiment of the LCD backlight apparatus accordingto the invention will be described by referring back to FIG. 1. Themeasurements of the diffusing plate 2 also vary depending on its stateof water absorption, namely the degree of humidity around it. Themaximum amount of water absorption of the diffusing plate 2 (saturationwater absorption) tends to increase with respect to humidity. Saturationwater absorption also has a positive correlation with the elongation ofthe diffusing plate 2. Thus, it must be estimated how much the diffusingplate 2 would be extended under maximum humidity conditions from itsmeasurements under normal humidity conditions. Calculations for thispurpose will be hereafter described by referring to FIGS. 17 and 18.

The influence of humidity on the diffusing plate 2 will be described byreferring to FIGS. 17 and 18. FIG. 17 shows an example of experimentaldata concerning the relationship between the number of days in which thediffusing plate 2 was left immersed in water and the water absorptionratio. FIG. 18 shows the relationship between the saturation absorptionratio and the length-increase ratio of the diffusing plate 2. Assumingthe maximum temperature of the LCD backlight is 60° C., the absorptionof the diffusing plate is determined to be 2.1% from FIG. 17. Thelength-increase ratio at absorption 2.1% is determined to be 0.45% fromFIG. 18. Thus, the increase in the interval of the left and rightopenings in the diffusing plate 2 can be calculated by thebelow-indicated equation. In reality, it is unlikely that the diffusingplate would be immersed in water. However, given the possibility ofusing the LCD apparatus in a very humid environment continuously for anextended period of time, a length-increase ratio of 0.45% wouldcorrespond to a worst-case assumption and can be therefore consideredsufficient from design perspective. Thus, the following equation can beintroduced:ΔL=200 mm×0.45/100=0.9 mm

In other words, in order to overcome the stress due to the weight of thediffusing plate itself, a gap of the order of 0.9 mm must be givenbetween the opening in the diffusing plate 2 and the locking projectionwhen taking extension due to humidity into consideration. The same canbe applied to the vertical direction.

More specifically, the diffusing plate 2 must be designed taking the twofactors of thermal expansion and moisture absorption into consideration.In general, the extension of the diffusing plate 2 due to moistureabsorption and its thermal expansion can be independently considered.Thus, the extension caused by temperature change and that caused byhumidity change can be added together, and the resultant value can beused for the gap between the edge of the opening and the periphery ofthe locking projection. An example of the method for this calculationwill be described below.

It is now assumed that the temperature of the diffusing plate 2 hasincreased from 20° C. (room temperature) to 60° C. after the diffusingplate 2 that had absorbed water to a saturation absorption level wasassembled in a panel module and the LCD apparatus was turned on. Theseconditions are the same as the two above-described conditions, and theycan be approximated by the sum of the two calculation results. Namely,the sum of the extension caused by thermal change and that caused byhumidity for the 200 mm opening interval can be calculated byΔL=0.6 mm+0.9 mm=1.5 mm

The same estimation can be made for the vertical direction as well.Based on these estimates, the positions of the openings can be designed.

Hereafter, the LCD backlight apparatus according to a fourth embodimentof the invention will be described by referring to FIG. 12.

As described above, the plastic diffusing plate 2 might be warped towardthe LCD panel due to its water absorption or thermal expansion ratioscombined with the thermal or humidity environments inside the backlighteven if its own weight does not have any influence. If such warpingbecomes excessive, the protruding portion of the diffusing plate cancome into contact with part of the LCD panel via the optical sheets 1,causing temperature irregularities to show on the entire LCD panel.These temperature irregularities may in turn produce luminanceirregularities on the entire panel screen. Thus, in order to preventsuch warping of the diffusing plate toward the LCD panel, a stopper 8 inthe shape of a bracket or ko (

Japanese character (KATAKANA)) shape, for example, is used. The stopper8 should desirably be attached at such a position that it can hold eachlocking projection 3 a inner surface of the ko

character shape, between its two legs in the direction corresponding tothe thickness of the panel.

In this way, the diffusing plate's degree of spatial freedom in thedirection corresponding to thickness can be restricted without causingstress on the diffusing plate 2 or the optical sheets 1 in the directioncorresponding to thickness. Thus, even if the diffusing plate 2 iswarped toward the LCD panel, the possibility of the plate's coming intocontact with the LCD panel can be minimized. Preferably, instead of theko

character-shaped stopper 8, an L-shaped one that comes into contact withthe optical members on the LCD panel side but not with their back may beused. By using such an L-shaped stopper, the optical members can beprevented from warping toward the LCD panel even if they are warped.

Hereafter, a fifth embodiment of the LCD backlight apparatus accordingto the invention will be described. In this embodiment, the diffusingplate is provided with an antistatic function. The diffusing plate withan antistatic function is produced by mixing an antistatic agent duringthe manufacture (in the polymerization step) of the diffusing plate.This feature prevents the contamination of the diffusing plate byimpurities during its storage and assembly into a module, so that thedeterioration of its quality due to the adhesion of dust or dirt can beprevented.

Hereafter a method of manufacturing the LCD backlight apparatusaccording to a sixth embodiment of the invention will be described. FIG.13 shows an example of the diffusing plate in the present embodiment.The direct backlight apparatuses are often used in large-sized displays.In the case of apparatuses using an optical guide plate, the weightproblem is pronounced. Specifically, as the size of the edge-lightingtype backlight apparatus increases, so must the optical guide plate beincreased in thickness, thus increasing its weight. In contrast, adirect backlight apparatus can maintain its strength by the surroundingstructures, thus requiring less thickness than an apparatus using anoptical guide plate even when increased in size. Thus, direct backlightapparatuses can be increased in size while reducing their weight.

However, the ease of handling of direct backlight apparatuses could alsosuffer, particularly when they have large sizes. For example, the levelof safety during operation might drop, or the productivity might becompromised. Accordingly, in the present embodiment, the edges and sidesof the diffusing plate are beveled. By thus forming beveled portions M,the diffusing plates can be handled safely and speedily by those whomanufacture them, thus increasing the quality of the products.

Advantages of the LCD backlight apparatus according to the variousembodiments of the invention are as follows. The size of the backlightapparatus in LCD apparatuses can be increased, because the warping ofthe optical diffusing sheets due to their own weights can be prevented.The influence of the weight of the optical sheets or diffusing plate onthemselves can be reduced when the display apparatus is rotated by 180°or 90° in the display plane, so that the warping of those opticalmembers by their own weights can be prevented. By supporting the opticalmembers using the openings and locking projections at the top instead ofat the bottom, the stress applied to the openings by the weight of theoptical members can be reduced, so that the deformation of such membersdue to the stress applied to their openings can be prevented. Theproblems caused by thermal expansion and/or water absorption in theoptical sheets or diffusing plate can be prevented.

By holding the optical members by ko

character-shaped or L-shaped stoppers at their edges, the warping of theoptical members toward the LCD panel can be prevented. By providing thediffusing plate with an antistatic function, the adhesion of dust ordirt on the optical members due to their static can be prevented. Bybeveling the edges or sides of the diffusing plate, the plate can bemade safer to handle, thus contributing to the improvement in itsreliability and quality.

While in the various embodiments of the invention as described above theopenings are formed in the optical members and the locking portion areformed in the frame (lamp holder), the openings may be formed in theframe and the locking projections in the optical members. The inventioncan also be applied to relatively small-sized lighting or LCDapparatuses of the light-guiding plate type (or an edge-lighting typewhere light sources are disposed on either side of the light-guidingplate). The backlight apparatus may be provided with a known rotatingmechanism so that it can be rotated and stopped at arbitrary angles,rather than at fixed angles (such as at 90° intervals) as describedabove. Further, instead of or together with the rotation in the displayplane, the lighting or backlight apparatus according to the inventionmay be allowed to be rotated about an axis including and intersectingthe screen. In this case, too, it is desirable that the optical membersbe supported above their center of gravity so that their warping can beprevented at any rotation position, as described in the embodiments.

It should be obvious to those skilled in the art that variations,modifications or combinations are possible.

INDUSTRIAL APPLICABILITY

Thus, in accordance with the invention, the optical members such asoptical sheets and diffusing plate in the lighting or LCD backlightapparatus can be locked when the entire display is rotated about an axisnormal to the screen plane. Further, the warping of such optical membersdue to their own weight can be prevented. The warping of the opticalmembers can be prevented under various environments by taking intoconsideration the thermal expansion or other properties of the opticalmembers.

Thus, clear display can be realized with few luminance irregularities.

1. A lighting apparatus, comprising: an optical member; and a pluralityof locking portions, wherein, a light emitting plane of the opticalmember is parallel to a vertical direction and at least one opening isprovided in each of four regions of the optical member that aredemarcated by a line parallel to the vertical direction that passesthrough the center of gravity of the light emitting plane of the opticalmember and a line parallel to a horizontal direction that passes throughthe center of gravity, in each of the four regions, a locking portionpenetrates a corresponding opening, regardless of which two adjacentregions of the four regions are positioned vertically above with respectto the center of gravity when the lighting apparatus is set, the opticalmember is suspended by the locking portion penetrating the correspondingopening in a vertically upper and horizontally left region with respectto the center of gravity, and by the locking portion penetrating thecorresponding opening in a vertically upper and horizontally rightregion with respect to the center of gravity, as an upper peripheralportion of each locking portion abuts on an upper-edge portion of thecorresponding opening, and in a vertically lower side with respect tothe center of gravity of the optical member, each of the lockingportions penetrates the corresponding opening such that the opticalmember is not subjected to the stress caused by its own weight in thevertically upward direction, nor is it subjected to the stress caused byits contact in the vertically downward direction with the lockingportion.
 2. The lighting apparatus according to claim 1, wherein,regardless of which two adjacent regions of the four regions are locatedabove with respect to the center of gravity when the lighting apparatusis set, in a lower side with respect to the center of gravity of theoptical member, said each of the locking portions penetrates thecorresponding opening in a contactless manner.
 3. An LCD apparatuscomprising the lighting apparatus of claim 1 and an LCD panel.
 4. Alighting apparatus comprising: an optical member having a plurality ofopenings; and a plurality of locking portions, the lighting apparatuscomprising at least four sets of the opening and the locking portionthat penetrates the opening, wherein, either in a basic position of thelighting apparatus in which a light emitting plane of the optical memberis parallel with a vertical direction, or in a first stop positionthereof that is taken when the lighting apparatus is rotated from thebasic position in the plane of the optical member while the lightemitting plane of the optical member remains parallel to a verticaldirection, the optical member is suspended by at least one of the setsof the opening and the locking portion that penetrates the opening, asthey are engaged with one another in a vertically upper side withrespect to the center of gravity of the optical member, and in avertically lower side with respect to the center of gravity of theoptical member, each of the locking portions penetrates a correspondingopening such that the optical member is not subjected to the stresscaused by its own weight in the vertically upward direction, nor is itsubjected to the stress caused by its contact in the vertically downwarddirection with the locking portion.
 5. The lighting apparatus accordingto claim 4, wherein, either in the basic position of the lightingapparatus or in the first stop position, the optical member is disposedin a state such that the opening and the locking portion do not comeinto contact with one another in a vertically lower side with respect tothe center of gravity of the optical member.
 6. The lighting apparatusaccording to claim 5, wherein the state such that the opening and thelocking portion are not in contact with one another is a state suchthat, when the lighting apparatus is used in an LCD display apparatus,the optical member is given a degree of spatial freedom within the rangeof the expansion of the optical member that is caused by thermalexpansion and/or absorption of moisture in the optical member within thenormal range of use of the LCD apparatus.
 7. The lighting apparatusaccording to claim 4, wherein, either in the basic position or in thefirst stop position, the opening is shaped longer in the left-rightdirection than in the vertical direction with respect to the center ofgravity in the upper side of the optical member in the verticaldirection with respect to the center of gravity, wherein the lockingportion that engages with the opening has its upper peripheral portioncome into contact with the opening in a longitudinal direction of theopening.
 8. The lighting apparatus according to claim 4, wherein thefirst stop position is a position that is taken when the lightingapparatus is rotated by 90° from the basic position in the plane of theoptical member while the light emitting plane of the optical memberremains parallel with the vertical direction.
 9. The lighting apparatusaccording to claim 4, wherein the first stop position is a position thatis taken when the lighting apparatus is rotated by 180° from the basicposition in the plane of the optical member while the light emittingplane of the optical member remains parallel with the verticaldirection.
 10. The lighting apparatus according to claim 4, wherein thesurface of the optical member is provided with an antistatic finish. 11.The lighting apparatus according to claim 4, wherein at least a corneror a side of the optical member is chamfered.
 12. An LCD apparatuscomprising the lighting apparatus of claim 4 as a backlight apparatus,and an LCD panel as a display unit.
 13. The LCD apparatus according toclaim 12, further comprising a rotating mechanism for rotating thedisplay unit.
 14. A lighting apparatus comprising: an optical memberhaving a plurality of cutout portions; and a plurality of lockingportions associated with the cutout portions, wherein, a light emittingplane of the optical member is parallel with a vertical direction, thecutout portions are formed in the each end-sides of the optical memberat the top, bottom, left, and right of the optical member with respectto the center of gravity of the light emitting plane, such that thecutout portions can be engaged with the locking portions, and regardlessof which of the top, bottom, left, and right end-sides comes at the topwhen the lighting apparatus is set, the optical member is supported byan upper internal edge of each of the cutout portions in the left andright end-sides of the optical member abutting on the locking portionadapted to be engaged with the cutout portion.
 15. The lightingapparatus according to claim 14, wherein, in cases where the lightemitting plane of the optical member is parallel with the verticaldirection, at least one of the cutout portions formed in both left andright sides horizontally of the optical member is disposed in avertically upper side with respect to the center of gravity of theoptical member.
 16. The lighting apparatus according to claim 14,wherein, both in a basic position of the lighting apparatus where alight emitting plane of the optical member is parallel with a verticaldirection, and in a first stop position that is taken when the lightingapparatus is rotated from the basic position in the plane of the opticalmember while the light emitting plane of the optical member remainsparallel with the vertical direction, the optical member is supported byan upper internal edge of each of the cutout portions in the bothend-sides that are positioned in the horizontal direction in the opticalmember abutting on the locking portion adapted to be engaged with thecutout portion.
 17. An LCD apparatus comprising the lighting apparatusof claim 14 and an LCD panel.